LiFePO4 Versus Lead-Acid For Deep Cycle Work

The comparison that matters is not the price per amp hour on the label. It is the price per usable amp hour over the life of the installation, and on that basis the two chemistries are not close.

Usable Capacity Is The First Difference

Discharging a flooded or AGM lead-acid battery below 50% shortens its life sharply, so a 200Ah lead-acid bank is a 100Ah bank in practice. Our 12V LiFePO4 packs publish 95-100% depth of discharge, which is why a 100Ah lithium pack does the same daily work as a 200Ah lead-acid bank and why the product pages describe it as more usable power, up to 2X with a higher DOD.

Weight And Space

The published figures on our own range make the point: a group 24 12V 100Ah pack is 9.7 kg, a 12V 150Ah pack is 14.2 kg and a 12V 200Ah pack is 18.4 kg. Each is around a third of the weight of the equivalent lead-acid battery. On a boat or an RV that weight is payload; in a rack it is what one person can lift.

Charge Acceptance Changes The System Design

Lead-acid takes a long absorption stage at the top of the charge, which is why a solar array that looks big enough on paper never quite refills the bank. LiFePO4 accepts 0.5C to 1C, so the same array puts its harvest into the battery in one to two hours rather than trickling all afternoon. That single property is often worth more than the extra capacity.

• Charger must have a LiFePO4 profile - an equalisation stage at 15V or more will trip the BMS
• Alternator charging needs a DC-DC charger, because a lithium pack will draw everything the alternator can give
• Solar controllers need the lithium absorption and float voltages set, not the AGM defaults
• A battery monitor reading amp hours is more useful than a voltmeter, because the lithium discharge curve is almost flat

Cycle Life Over A Realistic Horizon

Our deep cycle range publishes 3000+ cycles, and the 51.2V energy storage range publishes 6000+. The product pages describe that as six to eight times the cycle life of a comparable lead-acid battery. Cycled once a day, 3000 cycles is over eight years of service.

Where Lead-Acid Still Wins

Engine cranking is the clear case. Our automotive-case packs state plainly that they are energy storage batteries and must not be used for starting. Very cold charging without a heater is another: lead-acid tolerates it, LiFePO4 does not. And for a battery that will be cycled a handful of times a year, the lifetime maths that justifies lithium never gets a chance to run.

If you are replacing a bank, send us the tray dimensions, the charger model and the daily load. The answer comes back as a pack and a charging change, not a catalogue page.